One prevalent example of a translucent object is a container formed from translucent materials. Examples of such translucent materials include glass and plastic. Such containers are commonly used to house various products, such as beverages. One common type of translucent container which is used for this purpose is a glass bottle.
The manufacture of glass bottles begins with the preparation of raw materials. Sand and soda ash are measured in precise quantities, mixed together and conveyed to storage silos located over large melting furnaces. The mixed materials are continuously metered into the furnaces to replace molten glass which is dispensed from the furnaces after melting.
The furnaces are heated by a combination of natural gas and electricity and are operated at a temperature of over 2500 degrees Fahrenheit. The melted mixture of raw materials forms molten glass which flows from the furnaces through refractory channels, also known as forehearths, to a position over bottle forming machines.
A bottle forming machine known in the industry as an "I.S. machine" draws the glass into individual gobs and drops each gob into a blank mold. The blank mold forms a bottle preform, also referred to as a parison. The preform is transferred to a blow mold where it is blown by compressed air into a bottle. Each blow mold cavity typically contains indicia provided on a bottom wall thereof which embosses each bottle with code characters indicating the mold cavity in which it was formed.
The molds are lubricated by oil-borne carbon. The hot mold vaporizes the oil and some of the carbon immediately upon contact, leaving most of the carbon deposited upon the mold. Thus, the area around the mold is an extremely dirty environment filled with oil and carbon vapors and condensate.
An I.S. machine typically has between six and sixteen individual sections, with each section having from one to four blow mold cavities. Each section may be capable of manufacturing one to four bottles at a time. A typical eight section, triple gob, I.S. machine used in the production of beer bottles may produce 270 beer bottles per minute.
After the bottles have been blown, they are transferred from the respective blow mold cavities onto a moving conveyor belt. The bottles are positioned on the moving conveyor belt in a single line in a sequence corresponding to the sequence of the blow mold cavities in which the bottles were formed. The finished bottles transferred onto the conveyor from the blow mold are still red hot (approximately 1,000 degrees Fahrenheit). These hot bottles are conveyed by the conveyor belt through a hot end coating hood where they are chemically treated with a stannous chloride compound for strengthening. Vapors from the hot end coating hood also contribute significantly to the harsh environment found at the "hot end" of the bottle production line.
After passing through the hot end coating hood, the hot bottles are conveyed through an annealing oven or lehr where they are reheated and then cooled in a controlled manner to eliminate stresses in the glass. This annealing process typically takes from 20 to 30 minutes. The annealing process is the last process which takes place at the hot end of the production line. The portion of the production line downstream from the annealing oven is referred to as the "cold end" of the production line. In contrast to the hot end, the cold end is neither hot nor dirty. At the cold end of the production line, bottles are conveyed through a series of inspection devices. Typical prior art inspection devices include a squeezer which physically squeezes each bottle to check its sidewall strength. Another prior art cold end inspection device is referred to in the industry as a total inspection machine or T.I.M. which is sold by Emhart Glass having a business address at 1140 Sullivan Street, Elmira, N.Y. 14902. The total inspection machine physically engages each bottle and checks the size of the bottle neck opening and the thickness of the bottle sidewall and reads the code on the bottle bottom wall to determine the mold of origin. On a statistical sampling basis, the T.I.M. also sends bottles off line to be tested for burst strength, weighing, and measuring. Reports generated from the T.I.M. correlate bottle defects with the mold of origin. Another typical prior art inspection device is known as a "super scanner" sold by Inex, 13327 U.S. 19 North, Clearwater, Fla. 34624. The super scanner operates on a sample of bottles which are removed from the bottle production line. It initially scans a bottle, then engages and rotates the bottle approximately 90 degrees and scans it again. The super scanner uses image analysis to perform certain dimensional parameter checks of the bottle.
At both the T.I.M. and the super scanner inspection stations, defective bottles may be rejected by a cold end rejection device. After passing through the cold end inspection stations, bottles are transferred to a case packer machine, placed into a cardboard carton and conveyed to a palletizer machine for being placed in pallets. Loaded pallets are then shipped to a filling facility, such as a brewery.
Translucent objects often contain defects which may be formed, for example, during the manufacture of the objects. In the case of glass bottles, for example, foreign matter is sometimes present in the glass batch. Such foreign matter, e.g., steel or quartz particles, may eventually find its way into the walls of a bottle, thus creating a flaw in the bottle. Such flaws are commonly referred to as "stones" in the glass making industry. Stones are undesirable because they may weaken the bottle walls and because they detract from the aesthetic appearance of the bottle.
Another flaw which sometimes occurs in glass bottles is commonly referred to in the glass bottle making industry as a "hollow neck" bottle. A hollow neck bottle is one in which the glass forming the neck area of the bottle is too thin. This condition is undesirable in that it causes the bottle neck to be relatively weak. Hollow neck bottles are most likely to occur when a common glass bottle manufacturing technique known in the glass making industry as "press and blow" is used.
In the case of a typical hollow neck defect, the outer wall of the bottle neck is generally formed having the proper diameter. The inner wall, however, is formed having too large a diameter, such that the bottle wall thickness extending between the inner and outer walls is too thin. Because the outer wall is usually formed having the proper diameter, bottles containing a hollow neck defect generally appear to be normal, i.e., non-defective, when viewed from the outside thereof. This aspect makes hollow neck defects difficult to detect with conventional bottle inspection devices and methods which generally analyze only the outer periphery of the bottle.
It is desirable to detect and reject glass bottles having flaws, such as the specific flaws described above. In the past, several methods and devices for inspecting glass bottles have been developed. One type of bottle inspection system is an imaging system, where, for example, an imaging device, such as a camera, images bottles as they pass by on a conveyor belt. Examples of such imaging inspection systems are disclosed in U.S. Pat. No. 5,437,702 of Burns et al.; U.S. patent application Ser. No. 08/914,984 of Philip J. Lucas for HOT BOTTLE INSPECTION APPARATUS AND METHOD filed Aug. 20, 1997; U.S. patent application Ser. No. 08/526,897 of Philip J. Lucas for HOT BOTTLE INSPECTION APPARATUS AND METHOD filed Sep. 12, 1995; U.S. Pat. No. 5,734,467 of Philip J. Lucas and in U.S. patent application Ser. No. 09/001,215 of Philip J. Lucas for METHOD FOR INSPECTING MANUFACTURED ARTICLES, filed Dec. 30, 1997, the disclosures of which are all hereby incorporated by reference for all that is contained therein.
Such imaging systems are capable of performing high-speed "real time" inspection of bottles. The Burns et al. and Lucas systems described above, however, are primarily directed only to the inspection of dimensional attributes such as bottle diameter or bottle lean. Neither the Burns et al., nor the Lucas systems are specifically directed toward the detection of defects which occur within the envelope of the bottle, e.g., the hollow neck and stone type defects discussed previously.
Another type of bottle inspection system is a light transmittance measuring system, where, for example, a probe is inserted into a bottle in order to measure the amount of light which passes through specific portions of the bottle wall. Examples of such a light transmittance measuring system are disclosed in U.S. patent application Ser. No. 08/898,766 of Dennis K. Hidalgo et al. for METHOD FOR MEASUREMENT OF LIGHT TRANSMITTANCE filed Jul. 23, 1997, and in U.S. patent application Ser. No. 08/698,591 of Dennis K. Hidalgo et al. for METHOD FOR MEASUREMENT OF LIGHT TRANSMITTANCE filed Aug. 16, 1996, the disclosures of which are both hereby incorporated by reference for all that is contained therein.
Such a light transmittance inspection system is capable of detecting variations in color density within the walls of the bottle. Because a probe must be inserted into each tested bottle, however, this system is not well-suited for high-speed "real time" inspection of bottles.
Accordingly, it would be desirable to provide a high-speed inspection system which is capable of detecting flaws existing within the envelope of translucent objects such as glass bottles.